Observations

Description

Valves are linear-lanceolate, with very slightly constricted apices. Populations often exhibit a narrow size range. Areolae are round or oval. They form transverse striae that are radiate at the center of the valve and slightly or strongly convergent near the apices. Striae circumradiate the apices. The single row of areolae closest to either side of the raphe forms a continuous line that begins and ends at the poles and curves around the rounded central area. This feature is distinct under the light microscope, especially at the central area. Small, irregularly spaced poroids are present in the central area or near the raphe. The raphe branches and longitudinal ribs are slightly curved. The longitudinal ribs fuse with the helictoglossae to form a porte-crayon. These longitudinal ribs are incomplete at the central nodule. The central nodule is relatively flat. The external proximal and distal raphe ends form a small Y-shape, a feature observable with electron microscopy. The shape of the central area is generally ovoid, and the size of the central area may vary within a population.

These records of Frustulia asiatica are from Hawaii. To date, this species has not been documented from the continental US, however F. asiatica can be compared to populations in California. We have observed California specimens that are similar in morphology to both F. asiatica and F. vulgaris. Further work may be needed to determine if the California specimens are a separate species.

Unlike most species of Frustulia, F. asiatica has longitudinal ribs that are incomplete at the valve center. The valves are linear-lanceolate and not at all rhomboid like other Frustulia taxa, but linear-lanceolate in shape. The central area is oval.

Compare

Frustulia asiatica is distinguished from F. vulgaris by its narrower valves and less protracted apices. In addition, the small, irregular poroids adjacent to the raphe in F. asiatica (visible only with SEM) have not yet been observed in US populations of F. vulgaris.